1. Field of the Invention
The present invention relates to a fuel cell stack having a fuel cell unit including at least first and second electrolyte electrode assemblies and at least first to third separators sandwiching the first and second electrolyte electrode assemblies. Each of the first and second electrolyte electrode assemblies includes a pair of electrodes and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (electrolyte electrode assembly) which includes two electrodes (anode and cathode), and a solid polymer electrolyte membrane interposed between the electrodes. The electrolyte membrane is a polymer ion exchange membrane (proton exchange membrane). The membrane electrode assembly is sandwiched between a pair of separators. The membrane electrode assembly and the separators make up a unit cell for generating electricity.
In the unit cell, a fuel gas such as a gas chiefly containing hydrogen (hereinafter also referred to as the “hydrogen-containing gas”) is supplied to the anode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions and electrons. The hydrogen ions move toward the cathode through the electrolyte membrane, and the electrons flow through an external circuit to the cathode, creating a DC electrical energy. A gas chiefly containing oxygen or the air (hereinafter also referred to as the “oxygen-containing gas”) is supplied to the cathode. At the cathode, the hydrogen ions from the anode combine with the electrons and oxygen to produce water.
In general, several tens to several hundreds of unit cells are stacked together to form a stack. At this time, the unit cells need to be positioned in alignment with each other accurately. For this purpose, in practice, knock pins are inserted into positioning holes of the unit cells. However, as the increase in the number of the stacked unit cells, the insertion operation of the knock pins becomes difficult, and thus, the fuel cell cannot be assembled efficiently. Further, the positional deviation of the members occurs easily, and the sealing function may not be achieved.
According to the disclosure of Japanese Laid-Open Patent Publication No. 2004-172094, a fuel cell includes an electrolyte electrode assembly and first and second separators sandwiching the electrolyte electrode assembly. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes. The first and second separators have first and second positioning holes, and first and second insulating positioning members are attached to the first and second positioning holes. The outer wall of the second insulating positioning member is fitted to the inner wall of the first insulating positioning member. Thus, the first and second separators are positioned in alignment with each other, while the first and second separators are insulated.
Further, the first insulating positioning member includes a support portion for supporting one surface of the first separator, and an expanded portion fitted to the first positioning hole of the first separator and having the internal wall. The second positioning member includes a support portion for supporting one surface of the second separator, a first expanded portion fitted to the second positioning hole of the second separator, and a second expanded portion expanding toward the side opposite to the first expanded portion, and having the outer wall.
The fuel cell (unit cell) has the electrolyte electrode assembly and the first and second separators sandwiching the electrolyte electrode assembly, and the conventional technique relates to the structure of positioning the first and second separators in alignment with each other.
However, recently, in order to reduce the number of components for reducing the overall size of the fuel cell stack, the so-called skip cooling type fuel cell is adopted. In the skip cooling type fuel cell, each of unit cells is formed by stacking two electrolyte electrode assemblies and three separators alternately. The electrolyte electrode assemblies are sandwiched between the separators. A coolant flow field is formed at each of positions between the fuel cell units. The fuel cell units are stacked together to form a fuel cell stack.